This invention relates to a continuous deoderizing apparatus of fat and oil, particularly, to those using superheated steam for heating fat and oil to a deodorizing temperature.
The conventional deoderizing system of fat and oil utilizes an organic heat transfer medium such as Dowtherm A, E (trade name by Dow Chemical Co., U.S.A.), SK oil (trade name by Soken Chemical Co., Japan), etc. for heating fat and oil. Such an organic heat transfer medium, however, is poisonous in general. Thus, in order to avoid the danger caused by the mixing of the medium into the eatable fat or oil, it has been strongly desired in the industries to develop suitable heat transfer media replacing organic heat transfer media. To this end, the present inventors previously developed a deodorizing method of fat and oil utilizing hot combustion gases as a heat transfer medium and filed a patent application for the technique (Japanese Patent Application No. 58,409/73). This method can be applied to an existing deodorizing apparatus by a simple revamp, but the requirement of a relatively large gas recirculation equipment renders the method not quite satisfactory when it comes to a large newly installed deodorizing system.
Besides the hot combustion gases mentioned, conceivable as heat transfer media replacing the organic heat transfer media are high pressure steam of 100 to 130 kg/cm.sup.2 G and hot, pressurized water of 200 to 300.degree. C. These media, however, present problems with respect to the safety in the handling because of their pressures.
The present inventors made an attempt to utilize as the heat transfer medium for heating fat and oil the operating steam of a steam ejector acting as a vacuum producing device for a deodorizing apparatus of fat and oil. The pressure of the operating steam of a steam ejector is in general as low as 8 to 12 kg/cm.sup.2 G but is high enough to prevent use of a blower or the like. Clearly, the use of such a steam facilitates the operation and maintenance of the apparatus to a markedly high extent. But, it should be noted in this connection that a majority of conventional deodorizing apparatus are of semi-continuous type. In such systems, it is substantially impossible to recover heat from the product stream. It follows that, in order to heat the feedstock fat and oil to a deodorizing temperature by only the steam required for the operation of a steam ejector the steam must be heated up to 600.degree. C or higher. Indeed, it is possible to use a steam of somewhat lower temperature, but in such a case a large amount of steam is required for heating the feedstock up to a deodorizing temperature. It should also be mentioned that the feedstock fat or oil is intermittently heated in a semi-continuous type apparatus. This presents a problem. Where the heating capacity of a steam superheater used is relatively small, it is difficult to maintain a stable operation of the apparatus. In conclusion, it was quite difficult to utilize successfully the operating steam of a steam ejector in a semi-continuous type deodorizing apparatus, in which it is impossible to recover heat from the deodorized product stream.